The present invention relates to a low-contaminative hose that permits a fluid to be passed therethrough with an absolutely minimal level of fluid contamination, and further to a rubber composition for use in producing such a hose.
Due to the problems with environmental pollution, the exhaustion of petroleum resources and the like, an impetus has been gathered in recent years to develop fuel cell-powered vehicles. A fuel cell is designed to receive, via supply pipes, a fuel gas typified by hydrogen or methanol, source of oxygen typified by air, and a cooling liquid typified by water or glycol. Thus, in the fuel cell, hydrogen component of the above fuel gas is allowed to react with oxygen component of the above air, thereby generating electrical energy. Unreacted components of the above fuel gas and unreacted air are released from the fuel cell through their respective exhaust pipes and then put back into their respective supply pipes. The above cooling liquid, which is being circulated in the fuel cell, is released through its exhaust pipe, followed by cooling and returns to its supply pipe.
A single cell in the fuel cell is generally structured with electrodes fitted thereto, which electrodes are formed by coating a catalyst such as platinum or the like on both sides of a plate-like electrolyte. The two electrodes are further connected to externally disposed electrical conductors. Electricity generation is performed with the fuel gas supplied to one such electrode, i.e., a negative pole, and with the air supplied to the other, i.e., a positive pole. More specifically, the fuel gas is decomposed by the action of the catalyst into hydrogen ions, i.e., protons, and electrons at the negative pole so that the hydrogen ions migrate to the positive pole after passage through the above-mentioned electrolyte, and the electrons migrate to the positive pole after passage through the above-mentioned external conductors. At the positive pole, the oxygen gas contained in the air is catalytically reacted with the hydrogen ions and electrons that have been migrated to that pole as stated above, whereby water is produced. Such a single cell structure acts as a fuel cell because an electric current flows upon migration of the above electrons.
However, in situations where ion extraction occurs from transport pipelines including the above supply pipes, exhaust pipes and the like, fluids such as a fuel gas and the like passing through the pipelines become mixed with and contaminated by the extracted ions. This causes contamination of the electrolyte, catalyst and the like in the above-described fuel cell, thus causing failure in the proper migration of hydrogen ions, decomposition of fuel gas and production of water during electricity generation. The fuel cell, therefore, suffers from poor efficiency in electricity generation and a considerable decline in output.
As another serious problem resulting from the ion extraction from each transport pipe, the fluid itself running through the pipeline becomes easily electrically conductive, and therefore, the fuel cell is liable to produce electrical leakage outwardly through the fluid. This electrical leakage is responsible for inefficient electricity generation in the fuel cell and also for generating hazardous electrical shocks to human beings.
Similar consequences occur, in addition to the transport pipes used in a fuel cell, in transport pipes for cooling liquids used in super computers, as well as in transport pipes for membrane cleaning liquids used in analytical instruments, and in the transport pipes for chip or wafer cleaning liquids used in semiconductor production. Namely, in the case of ion extraction arising from a cooling liquid-transport pipe used in such a super computer, the cooling liquid flowing through that pipe tends to become easily electrically conductive due to the extracted ions. Thus, the super computer is likely to produce outward electrical leakage, or produce improper operating signals. Furthermore, in the case of ion extraction arising from a membrane cleaning liquid-transport pipe used in such an analytical instrument, the membrane tends to be contaminated by the extracted ions, thus failing to ensure accurate analysis. And furthermore, in the case of ion extraction arising from a chip cleaning liquid-transport pipe used in semiconductor production, the semiconductor chips tend to be contaminated by the extracted ions, thereby frequently producing defective chips.
From the standpoint of good assembly working, it has been demanded that each such transport pipes be formed from a flexible material, that is, a hose.
The present inventors have made intensive studies in order to prevent a fluid running through a hose from being contaminated by the hose itself. In the studies, an approach has been centered on using at least one rubber selected from among an ethylene-propylene-diene terpolymer, an ethylene-propylene copolymer and a silicone rubber, and it has been found that when one such rubber is vulcanized using a peroxide as a vulcanizing agent, the use of a vulcanization accelerator such as a metal oxide or a metal hydroxide can be omitted, which accelerator is required for a rubber to be sulfur-vulcanized, and that the resultant hose is less likely to extract ions, which are eventually mixed in the fluid being passed through the hose. From further studies, it has also been found that when the above-noted rubber is subjected to peroxide vulcanization in the presence of a filler having a laminar crystal structure, a hose is formed which can more reliably alleviate ion extraction with respect to a fluid passing through the hose. These findings have led to the present invention. Here, the reason why such a filler with a laminar crystal structure is effective in making the hose much more resistant to ion extraction would presumably be attributable to the fact that the ions, even if extracted, are brought into an entrapped condition between the layers arranged to constitute the above-mentioned laminar crystal structure.
Accordingly, one object of the present invention is to provide a low-contaminative hose that permits a fluid to be passed therethrough at an absolutely minimal level of fluid contamination. Another object of the invention is to provide a rubber composition used in producing such a hose.
According to one aspect of the subject invention, a low-contaminative hose is provided which includes as essential components
(A) at least one rubber selected from the group consisting of an ethylene-propylene-diene terpolymer, an ethylene-propylene copolymer and a silicone rubber;
(B) a peroxide vulcanizing agent; and
(C) a filler having a laminar crystal structure.
According to another aspect of the present invention, a rubber composition for use in producing such a low-contaminative hose is provided which includes as essential components,
(A) at least one rubber selected from the group consisting of an ethylene-propylene-diene terpolymer, an ethylene-propylene copolymer and a silicone rubber;
(B) a peroxide vulcanizing agent; and
(C) a filler having a laminar crystal structure.
The present invention will now be described in greater detail and with regard to preferred embodiments.
One embodiment of the low-contaminative hose according to the invention can be achieved using a specific rubber composition. This rubber composition includes, as essential components, a selected rubber (component A), a peroxide vulcanizing agent (component B) and a filler having a laminar crystal structure (component C).
The selected rubber (component A) is chosen from an ethylene-propylene-diene terpolymer (hereinafter denoted by xe2x80x9cEPDMxe2x80x9d), an ethylene-propylene copolymer (hereinafter denoted by xe2x80x9cEPMxe2x80x9d) and a silicone rubber. These rubbers may be used singly, or two or three rubbers may be used in combination. EPDM is not specifically limited so long as it can be suitably used as a base material for the above-mentioned rubber composition. However, it is preferred that the EPDM have an iodine value of 6 to 30 and an ethylene content of 48 to 70% by weight. In particular, the iodine value more preferably is in the range of 10 to 24, while the ethylene content more preferably is in the range of 50 to 60% by weight.
No particular limitation is placed on the diene monomer, i.e., the third ingredient, for use in EPDM, but a diene monomer with 5 to 20 carbon atoms is preferred. Specific examples of the diene monomer include 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene, 1,4-octadiene, 1,4-cyclohexadiene, cyclooctadiene, dicyclo-pentadiene (DCP), 5-ethylidene-2-norbornene (ENB), 5-butylidene-2-norbornene, 2-methallyl-5-norbornene, 2-isopropenyl-5-norbornene and the like. These diene monomers may be used singly, or two or more monomers may be used in combination. Of the diene monomers listed above, it is preferred that dicyclopentadiene (DCP) and 5-ethylidene-2-norbornene (ENB) be used alone or in combination.
The peroxide vulcanizing agent (component B), which is mixed with the selected rubber (component A), is chosen from, for example, 2,4-dichloro-benzoyl peroxide, benzoyl peroxide, 1,1-di-t-butylperoxy-3,3,5-trimethyl-cyclohexane, 2,5-dimethyl-2,5-dibenzoylperoxyhexane, n-butyl-4,4xe2x80x2-di-t-butylperoxy valerate, dicumyl peroxide, t-butylperoxy benzoate, di-t-butylperoxydiisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butylperoxyhexene-3 and the like. These peroxides may be used singly, or two or more peroxides may be used in combination. Of the peroxides listed above, di-t-butylperoxydiisopropylbenzene is particularly preferable as it is free of malodor.
The amount of the peroxide vulcanizing agent (component B) to be added preferably is in the range of 1 to 10 parts by weight and, more preferably, 3 to 7 parts by weight, based on 100 parts by weight of the selected rubber (component A). The unit, part or parts by weight, is hereinafter referred to as xe2x80x9cpartxe2x80x9d or xe2x80x9cpartsxe2x80x9d for the convenience of explanation. If component B is less than 1 part, sufficient vulcanization is not attained so that the resultant hose is conducive to poor sealing properties. Conversely, if component B is more than 10 parts, the hose tends to become too hard to achieve adequate hose functions because it has too low an elongation at break, or too high a compression set.
The filler (component C), which is mixed with component A and component B, should be of a laminar crystal structure. The filler includes, for example, clay, talc, kaolinite, hydrotalcite, mica and the like. These fillers may be used singly, or two or more fillers may be used in combination. In view of its mechanical properties and molding properties, component C preferably has a mean particle diameter of 0.05 to 20 xcexcm and, more preferably, 0.1 to 10 xcexcm.
The amount of the filler (component C) to be added preferably is in the range of 20 to 130 parts and, more preferably, 40 to 110 parts, based on 100 parts of the selected rubber (component A). If component C is less than 20 parts, the resultant hose has a low electrical resistance, potentially causing electric leakage when it is used in a system where an electric current must be distributed, such as a fuel cell, a super computer or the like. Conversely, if component C is more than 130 parts, the hose tends to suffer poor resistance to ion extraction relative to a fluid placed in contact with that hose so that the fluid becomes easily contaminated with the extracted ions.
To the specific rubber composition according to the present invention, other components may be added, where desired, which include carbon black, paraffinic softeners and the like.
The specific rubber composition can be prepared by mixing components A to C with each other and, when necessary, with other components, and then by kneading the mixture using a kneading machine such as a roll, a kneader, a Banbury mixer or the like.
The low-contaminative hose according to the present invention can be formed, though not limited but for example, by extrusion-molding the above-described specific rubber composition using a mandrel, and thereafter by vulcanizing the whole extrudate, followed by drawing of the mandrel.
The low-contaminative hose thus formed typically has a thickness of about 1.5 to 12 mm depending on the uses of that hose. The inner diameter of this low-contaminative hose varies with the particular use, but usually ranges from about 5 to 50 mm.
The low-contaminative hose of the invention is structured such that a fluid to be passed therethrough is prevented from being contaminated by the ions extracted from that hose. Even in the case of using the hose as a transport pipeline for a fuel cell, the low-contaminative hose can therefore help minimize any possible reductions in electricity generation efficiency and in output of the fuel cell as well as any possible electric leakage. Furthermore, in the case of using the hose as a cooling liquid-transport pipe in a super computer, as a membrane cleaning liquid-transport pipe in an analytical instrument, and as a chip or wafer cleaning liquid-transport pipe in semiconductor production, the low-contaminative hose can eliminate the problems encountered in the conventional art as discussed earlier.
The low-contaminative hose of the present invention is not limited to the uses of the above-mentioned transport pipes. This hose can also be suitably applied to engine cooling hoses for various vehicles, such as a radiator hose used to connect an engine and a radiator, a heater hose used to connect an engine and a heater core, and other like hoses.
In particular, with regard to a low-contaminative hose that is formed by mixing the selected rubber (component A), the peroxide vulcanizing agent (component B), and the laminar crystal structure-having filler (component C) within the above-specified ranges of components, i.e., within 1 to 10 parts of component B and 20 to 130 parts of component C, respectively, per 100 parts of component A, such a hose can be extracted using pure water as a solvent such that the solvent reveals an electrical conductivity of 20 xcexcS/cm or less. Thus, even when a fluid is allowed to run through the low-contaminative hose, the fluid in itself is less electrically conductive. Therefore, the low-contaminative hose in accordance with such specified mixing ranges can yield excellent performance when it is used in a system where an electric current must be distributed, such as a transport pipe for the above fuel cell, or a cooling liquid-transport pipe for a super computer.
Furthermore, the low-contaminative hose in accordance with such specified mixing ranges met can be extracted in the same manner as stated above such that the solvent has a metal ion concentration of 0.5 ppm or less. Thus, even when a fluid is allowed to run through the low-contaminative hose, the fluid is less likely to be contaminated by the metal ions. In this respect, the low-contaminative hose formed within such specified mixing ranges can yield excellent performance when it is used as a transport pipe for the above fuel cell, a cooling liquid-transport pipe for a super computer, a membrane cleaning liquid-transport pipe for an analytical instrument, and a chip or wafer cleaning liquid-transport pipe for semiconductor production.
And further, the low-contaminative hose within such specified mixing ranges has, in itself, a volume resistivity of 107 xcexa9xc2x7cm or more, a surface resistivity of 108 xcexa9 or more, and an alternating electrical resistance (impedance) of 104 xcexa9xc2x7cm or more on flow of an alternating electric current of 104 Hz. Therefore, the low-contaminative hose is sufficiently high in electrical resistance. The low-contaminative hose within such specified mixing ranges, therefore, causes almost no electrical leakage even when it is used in a system where an electric current must be distributed, such as a transport pipe for the above fuel cell, or a cooling liquid-transport pipe for a super computer. Hence, this low-contaminative hose can yield excellent performance when in use as a transport pipe for a system that needs the distribution of an electric current.
In the foregoing embodiment, the specific rubber composition according to the invention has been formed into a low-contaminative hose in a tubular shape. Shapes of a sheet, a circle, a rod and the like are also acceptable which are capable of producing the same functions and effects as in this embodiment.
The following examples are given to further illustrate the present invention.